The increasing demand of wireless high data service has motivated various standards bodies such as the Third Generation Partnership Project 2 (3GPP2), the Third Generation Partnership Project (3GPP) and IEEE-802.16 to develop various wireless systems supporting faster data rate, higher spectral efficiency and more reliable communication such as Ultra Mobile Broadband (UMB), Long Term Evolution (LTE), and wireless Metropolitan Area Networks (MAN), respectively. Additionally, since multiple input, multiple output (MIMO) operation offers significant increases in data throughput and higher spectral efficiency without additional bandwidth or transmit power, MIMO is considered as an essential technology in providing the high data rate and increased system throughput in the various standard bodies.
Currently, LTE offers only MIMO in a downlink (DL) portion of a communications system, with support for up to two (2) codewords and four (4) transmit antennas, wherein DL refers to the transmission from the base station to a user equipment (UE). As used herein, a codeword refers to an encoded and modulated symbol sequence corresponding to an information block, such as the transport block defined in 3GPP specifications. No symbol-level channel interleaver was defined for LTE downlink because the time-frequency diversity due to the turbo internal interleaver and the rate matcher was found to be sufficient. Additionally, codeword to layer mapping was defined for LTE downlink without special consideration of successive interference cancellation (SIC) receiver.
In contrast to DL, only single antenna transmission is supported in LTE uplink (UL), i.e., transmission from the UE to the base station. Since single antenna transmission means that there is only one layer, LTE does not consider the transport block-to-layer mapping for UL. Due to the limited frequency diversity associated with single carrier frequency division multiple access (SC-FDMA), a symbol-level channel interleaver was defined for LTE UL. Without causing confusion, the symbol-level channel interleaver will be simply referred to as channel interleaver in the following. When upgrading LTE to LTE-Advanced, multiple-layer MIMO will be defined in order to reach the high throughput target. The processing defined for DL cannot be directly transferred to UL due to the different transmission scheme, orthogonal frequency division multiplexing (OFDM) for DL vs. SC-FDMA for UL. Thus there is a need to define channel interleaver and codeword-to-layer mapping that maximizes the throughput for the LTE-Advanced MIMO UL. In particular, the design needs to consider the usage of a SIC receiver in the base station, since the base station is able to handle more complexity than the UE.